Research in this section consists of studies on the physical and chemical properties of proteins of biological interest and the roles of ligand binding and protein-protein interactions in enzyme catalysis and regulation. 1. Interactions of divalent cations, substrates, and inhibitors with glutamine synthetase from E. coli have been studied by microcalorimetry and equilibrium dialysis techniques. 2. The interaction of the glutamine synthetase adenylyltransferase with various glutamine analogs was investigated. This enzyme, which catalyzes the adenylylation and deadenylylation of glutamine synthetase, has allosteric sites for both glutamine and the regulatory PII protien. 3. The glutamyl-tRNA synthetase from E. coli has been purified to homogeneity and found to be activated by a protein of approximately 74,000 mol. wt (74 K protein). The separation of these two proteins recently was achieved by preparative gel electrophoresis. A possible regulation of the glutamyl-tRNA synthetase (63,000 mol. wt.) by the 74K protein currently is being investigated.